Vapor pressures of the methanes

Experimental meas urements, not previously reported in detail, of the vapor pressure of CH, and the differe nces in vapor press ures of CH. and the deuterom ethanes below the normal boiling point are presented. A critical revi ew of the literature relating to the vapor pressures of m ethane and the deu teromethanes is given. On the basis of the experim ental measurem ents and t he previous literature t he following best values are assigned to fix ed points on the vapor pressure curves. The triple points are: CH., 87.50 mm , 90.66; CH aD , 84.5 mm , 90.41; CH 2D 2, 82. 0 mm, 90.17; CHDa, 80 .2 mm . 89.96; CD., 79.1 mm, 89.79 K. The boiling poin t of CH. is 111.67 K; the critical poin t 45.6 atmosp heres and 190.6 K. Equat ions and a table are given for t he vapor press ure of CH. in t he solid region , t he liquid region below t he normal boiling po in t and th e li qu id region above t he no rmal boiling poin t. The ratios of the vapor press ures of the methanes are expressed by equa t ions of th e form T log ,o PD/ PH = A -B/ T . Th e co ns ta nts A and B have t he follow ing va lues, r es pect ive ly: in t he solid range CH aD , 1.260, 110.2; CH2D 2, 2.694, 222. 2; CHDa, 4.452, 351.7; CD ., 5.529, 4 1.0.5 ; in t he liquid ra nge, CH aD , 1.328, 129.5 ; CH2D 2, 2.671 , 245.4; CHDa, 3.969, 343.8; C D., 5. 159, 42 1.1. Th e vapor-press ure ratios of the isoto pic m etha nes for m a nearl y geo metri c p rogressio n wi t h in creas ing d eute rium substitution. Dev ia t io ns of t heir mix t lll'eS fr om ideal solu t io ns arc very s ma ll. 1 This research was supported in part 'by the-Atom ic Energy Com mission . 2 Figures in brackets indicate t he li terat u re references a t) he end of t his paper.